A poor sequence for starting operation of a turbomachine engine may notably be expressed by poor ignition of the fuel-air mixture in the engine. The lack of ignition may have several origins, including insufficient fuel or even lack of fuel, metering, or injectors, or inadequacy or absence of energy, which may result from the degradation of the fuel pump or further from the system generating sparks.
Generally, the degradation of the system of the engine which comes into play in a sequence for starting the engine is monitored by means of the duration for igniting the fuel-air mixture, which is defined as the time interval between fuel injection into the combustion chamber of the engine and detection of the ignition of this mixture.
Thus, for a given engine, the ignition duration is used as an indicator of the degradation of the system used in the starting of an engine of a turbomachine. This indicator is therefore tracked over time, by a measurement at each starting of the engine, and an alert may be lifted in the case of confirmed deviation of the ignition duration with respect to a reference duration. It is then possible to anticipate possible of failures of the engine and to check the system in order to limit possible costs generated by non-starting of the engine.
For example, documents FR 2 942 001 and US 2007/026030 describe a method for monitoring the health condition of equipment involved in the starting capability of an engine, during which the ignition duration is inter alia determined and the obtained value is compared with an expected reference ignition duration for a reference engine, in order to infer therefrom if a piece of equipment of the engine has an anomaly.
However, the use of the ignition duration as an indicator is limited since its measurement exhibits a too large dispersion to be utilizable, given that it may vary according to the starting conditions of the engine without the system itself necessarily being modified. The graph of FIG. 1A, which shows the time-dependent change of the starting duration during five hundred consecutive starts for a given “sound” engine, i.e. undamaged, illustrates this dispersion, while the graph of FIG. 1B, which shows the smoothed time-dependency over five consecutive starts of this indicator, illustrates the noise resulting from this dispersion. Now, this noise is much too large for reliably detecting degradations of the starting system of the engine. The standard deviation is actually of the order of 1.2 so that only degradations of great intensity may be detected.
Document EP 2 256 319, as for it, describes a method for tracking performances of the engine during which various parameters are measured and then compared with values recorded beforehand in order to identify possible anomalies.
Generally, the monitoring methods of the prior art propose the monitoring of a large number of parameters in order to more easily identify the piece of equipment at the origin of the anomaly. Nevertheless, these methods are generally cumbersome to apply and require many sensors. Moreover, they do not give the possibility of sufficiently taking into account the environment of the engine, which may however affect the value of the parameters which are monitored without the pieces of equipment of the engine involved in its ignition however having been subject to degradations.